The Mojave river is interesting because for most of its length it
flows entirely underground. Looking at the wide, sandy, dry washes
along the many miles of its length you'd never suspect that a
year-round river was flowing beneath the surface.

One of the few places it comes to the surface is near Victorville, CA,
where a big chunk of rock gets in the way and forces the water to the
surface for a short distance before it disappears back into another
sandy wash.

That's all background to the interesting discovery we made at Alum
Rock park yesterday, where Penitencia creek and its tributary, Aguage
creek, have been looking progressively drier over this past month.

Walking upstream along the creek trail, we saw a fairly normal looking
lower creek up to the bridge at the last parking lot. Just a little
further upstream beyond that parking lot, the creek follows a series
of little cascades and pools. The pools are only a few feet deep at
this time of year ... but in one, we saw quite a large fish, about
a foot long and looking vaguely catfishy. How does something that
big live in a stream this shallow and ephemeral?

Not only that, but just upstream, as the stream crossed under the park
road near Sycamore Grove, it disappeared. We knew there had to be
water because something was feeding those pools and the lower creek --
but it was all underground here. We continued upstream, and discovered
... the Alum Rock Narrows! Right by the steel bridge over the creek,
the dry Penitencia and Aguage creeks become wet as water is forced to
the surface at their confluence, only to disappear again some fifty
feet downstream of the bridge.

It was very like the Victorville Narrows in miniature ... right here
in the big city. Not for the first time, I wish I could find a decent
geologic map of this fascinating park!